1. Field of the Invention
The present invention relates to an electronic ballast for a discharge lamp, comprising a drive circuit supplying high-frequency current to the lamp and including two power switches and control circuits therefor for controlling the power switches, such that the parallel half-waves of the lamp current pass through a first power switch and the reverse half-waves through a second power switch.
2. Problems in the Art
This type of drive circuits connected as a half-bridge are conventional in electronic ballasts for discharge lamps. As one example, reference can be made to the Applicant's U.S. Pat. No. 4,553,070. As prior art, reference can also be made to Patent publications U.S. Pat. No. 4,237,403, U.S. Pat. No. 4,277,728 and U.S. Pat. No. 4,370,600. A common feature to all these prior art circuit designs is that the control of power switches is based on information about the operation of the accompanying switch. This information is typically received from a transformer fitted in the lamp circuit. However, this involves a drawback of having to use a high-voltage differential in a control circuit, which is relative expensive to carry out whether using semiconductor technology or a transformer.